Thule Passive Lock Strap's unique design secures your trunk mounted racks to your car. It is two steel cables wrapped in a nylon sleeve attached to a tough round puck one end and a loop on the other end. You thread the strap around your bike rack frame, put the puck in the car trunk and close the trunk on the strap. Fits many styles and brands of racks. The strap is 4 feet long overall. This strap may have many other theft deterring applications. This is not a load securing device, it should only be used to prevent the theft of items that have been properly secured. Backed by Thule's Limited Lifetime Warranty. Manufacturer's part number: 533